Snap-acting switch contact actuating means for compressor governor



May 7, 1963 F. w. sHlRl-:Y

SNAP-ACTING SWITCH CONTACT ACTUATING MEANS FOR COMPRESSOR GOVERNOR Filed July 7, 1960 A T R E 7 -7.5:

INVENTOR. FRANK W. SHIREY A TrU/:INE/

` nite tent 3,089,603 SNAP-ACTING SWHTCH CNTACT ACTU/111W@ MEANS FR CMPRESSR QVERNQR Frank W. Shirey, Irwin, Pa., assigner to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation o1 Pennsylvania Filed July 7, 1966, Ser. No. 41,335 6 Claims. (Cl. 20th-82) This invention relates to electric circuit control switch apparatus and more particularly to a iiuid pressure operated control switch of the snap-acting type for interrupting with a minimum of arcing a circuit, such as that for an electric motor driving a fluid compressor.

ln present day motor-driven fluid compressors, motor control apparatus is commonly provided in which the motor is started and stopped by a fluid pressure operated electric control switch operative responsively to iluid pressure supplied under the control of .a conventional compressor governor, such `as the well-known Westinghouse Air Brake Company Type S governor. The governor operates responsively to variations of the stored reservoir pressure between maximum and minimum pressures of any desired range. The tluid pressure operated control switch comprises in part a switch operating piston operable to a switch-opening position when a piston chamber on one side thereof is supplied with fluid under pressure from the governor, to cause the switch contact members to open the motor circuit and thereby stop the motor `and the compressor driven thereby. When tiuid pressure in the reservoir reduces to a predetermined pressure, the usual high pressure valve of the governor is seated, and the uid under pressure acting on the switch operating piston in a piston chamber is vented via the governor. The switch operating piston is spring biased to restore the switch contact members to their closed position, thereby starting the compressor motor and continuing operation of the compressor until the fluid pressure has built up in the reservoir, at which time the governor operates in a well-known manner to supply uid under pressure to the aforementioned piston chamber to `act on the one side of the piston to cause the switch contact members to move to their open position as above mentioned.

With such apparatus, it has sometimes occurred that dirt, etc., in the high pressure valve chamber of the governor causes improper opening of the high pressure valve such that the fluid pressure is delivered to the piston chamber of the control switch at a reduced rate to cause slow opening of the contact members thereof. Another possible effect of dirt in the high pressure valve is improper seating of the high pressure valve, resulting in leakage of lluid under pressure past the said valve to the piston chamber of the control switch to cause a slow undesired fluid pressure build-up therein to in turn cause `a slow undesired opening of the switch contact members. The slow movement of the control piston caused `by the improper seating or opening of the high pressure valve of the governor, as just described, results in slow opening of the switch contact members and excessive arcing and burning of the main contacts to render them faulty and unable to complete the compressor motor supply circuitry when fluid pressure in the reservoir is low.

According to the present invention, there is provided a new `and improved switch apparatus having a snap action control of the switch contact members which produces a complete instantaneous breaking or opening of the main contacts upon establishment of a predetermined fluid pressure in the switch piston cham-ber acting on the switch control piston.

1n the accompanying drawing,

FIG. l is a diagrammatic view of a common lluid compressor system including an enlarged sectionalized View of the fluid pressure operated motor control switch device embodying the invention.

FIG. 2 is a fragmental section View of a limiting pin and groove arrangement used in the operating piston of the switch device.

Description Referring to FIG. 1 of the drawing, the fluid compressor motor control apparatus includes a uid pressure operated motor control switch device, hereinafter referred to as the switch device 1, utilized in cooperation with a standard compressor governor 2, to open or close the armature circuit of a direct current motor 3 used for driving a compressor 4 to charge a reservoir 5 with fluid under pressure as controlled by the governor 2. The armature circuit of the motor 3 includes a suitable source of D C. voltage represented by `a battery 6, a negative wire 7, and a positive wire 8 connected to terminal screw 9 and terminal cap nut 10, respectively, on the switch device 1 as shown partly dotted in the drawing. The terminal screw 9 is connected to a movable main contact 11 by way of jumper wire 12 and terminal cap nut 13, and the terminal cap nut lll -is connected to a stationary main contact 14, the opening and closing of said main contacts breaking or completing the `armature circuit respectively, as hereinafter explained. A manually operated switch 15 is connected in the postive wire 8 for connecting or disconnecting the armature circuit when the apparatus is to be put in service or taken out of service, respectively.

The compressor governor 2 shown in outline is of the W.A.B. Co. Type 5, similar to that disclosed in U.S. Patent 1,615,365 (assigned to the assignee of this application) with a single control passage connection between the governor and the switch device. An automatic drain valve 16 is connected to said control passage at the switch device to empty moisture from the device as necessary.

The switch device 1 comprises the usual components including the aforementioned stationary main contact 14 and movable main contact 11 mounted on the -free end of a contact arm 17 which is pivotally mounted `on a pin 18, said pin 1S being secured to the switch .body 19, and an operating piston Ztl movable to different positions within `a bore 21 responsively to a supply of uid under pressure thereto to operate cooperatively with a piston latch 22 to pivot the contact arm 17 and cause the main contacts 11 and 14 to be opened or closed.

The main contacts 11 and 1/5 are ofthe replaceable type so as to be renewed when badly burned or pitted by arcing therebetween. The movable main contact 11 is fastened to a pivotable Contact body 23 of insulating material by the terminal cap nut 13 and a terminal 24 molded in the body 23, said movable main contact 11 being biased toward the stationary main contact 14 by a contact insuring spring 2S, wherein the contact body 23 is given limited pivotal movement such that the contact insuring spring 25 insures a solid engagement between the two main contacts 11 and 14 when said contacts are closed. The stationary main contact #14 is secured by the terminal cap nut 161 to a terminal 26 molded in an insulating block 27. The insulating block 2'7 is of a molded glass-tilled polyester or similar insulating material and is secured to the switch body 19 by suitable means such as bolts 28 in a manner to electrically insulate the main contact 14- from the switch body 19.

Above and adjacent to the main contacts 11 and 14 is a pair of outwardly extending arcing contacts or arcing horns 29 and 30 for drawing out the arc resultant when the main contacts 11 and 1d are separated. The arcing horns 29 and 36 are of the usual type used in conventional switches with respective outer extremities thereof attached by suitable terminal screws 31 and 32 to jumper wires 33 and 34 connected to the respective main contacts 14 and 11. Surrounding the main contacts and arcing horns is a U-shaped arc chute 35 of a flame resistant insulating material with the usual appropriate arc diffuser and arc choppers 35a interposed between the sides of said yoke so as to assist in breaking up any arc between the main contacts and between the arcing horns. The structural and operational details of the arc chute and components not being pertinent to this invention, a full description thereof herein is deemed unnecessary. A detailed description may be had by reference to my copending application Serial No. 23,843, filed April 2l, 1960, now abandoned, and assigned to the assignee of the present invention.

The switch operating piston 2d is located in the lower part of the Switch device 1 within a cylindrical bore 21, preferably having a bushing or liner, in the switch body )t9 with a hollow piston stem -36 extending into a bore 37 coaxial to and of a diameter smaller than bore 21. The piston Ztl is slidably positioned within bore 21 in a manner to form a piston chamber 3S at one side of the face of said piston (the left side as shown in the drawing). The other side has the hollow piston stern 36 extending into the bore 37 to form a spring chamber 39 for housing a piston spring between said piston 2t? and a washer 41 seated on a circular lip 42 at the inner end (right end) of said bore for biasing saidfpiston toward the chamber 38. An O-ring 43 encircles the piston 2d in a groove to maintain a seal on the wall of bore 21 between the piston chamber 38 and the spring chamber 39.

The hollow piston stem 36 houses a contact operating rod `45 slidably fitted within a concentric bore 46 in said stem 36 and a trigger spring 47 positioned between the end of said concentric bore 46 and the closed end of a spring receiving bore 48 in said contact operating rod 45 in a manner to bias said contact operating rod 45 in a direction out of said concentric bore 46 to the right as shown in the drawing. A limiting pin 49 is inserted in said contact operating rod 45 and extends radially therethrough into a groove 50, as shown in FIG. 2, in the wall of said concentric bore 46 to limit Lthe movement of said contact operating rod 45 to the right in an outward direction relative to said concentric bore 46.

The-right-hand or inner end of the contact operating rod 45 is slotted or clevised to receive in the slotted portion thereof the piston latch 22, both the operating rod 45 and piston latch 22 being pivotally secured by a pin 51 to the contact arm 17 in a recess in said contact arm. The surface of the slotted portion of the contact operating rod 45 is sloped or tapered in a manner to engage the corresponding sloped inner edge of the piston latch when said piston latch is uncooked as hereinafter explained.

The outer end of the piston latch extends into bore 37 and is constructed with a lip S2 to latch in a cocked position over the washer 41 on the circular lip 42 of lthe inner end of bore 37 in response to the biasing forces of a spring 53. A spring 53 is interposed between the inner edge of the piston latch and the tapered surface in the slotted portion of the contact operating rod 45 in a manner to tend to maintain the two surfaces apart in a cocked position. An annular beveled surface 54 on the outer end of the piston stern 36engages an angular surface 55 on the outer or free end of the piston latch 22 when Ithe piston is moved to the right, thereby unlatching or uncocking the piston latch as hereinafter described.

Operation When the compressor is initially started with the systern not being charged with uid under pressure, the piston chamber 3S is void of fluid under pressure, and therefore the operating piston 2d' is initially in the extreme lefthand position in which it is shown with a stop disc 56 on the piston engaging a stop disc 57 on a piston chamber cover 58. With the piston 2t) in the extreme left-hand position, the force of spring 4t! acting through the medium ofpiston 26 and contact operating rod 45 causes the contact arm 17 to be pivoted about pin 18 to its closed position with the movable main contact 11 engaging the stationary main contact 14.

To initially start the compressor, the switch 15 is closed to complete the armature circuit for the motor 3, said circuit being traced from the positive terminal of the battery 6 via the switch 15, positive wire 8, terminal 25, stationary main contact 14, movable main contact 11 engaging the stationary main contact 14, jumper wire 12, to the terminal screw 9, and negative wire 7 to the motor armature and back to the negative side of the battery 6, thereby starting the motor 3` and compressor 4 in operation;

Being that there is no pressure in the reservoir 5, the high'pressure valve (not shown) of the governor 2 remains closed to permit a build-up of fluid under pressure in said reservoir. lt is in this period when the compressor is operating to build up the fluid pressure in the reservoir that any leakage past the governor high pressure valve would cause undesired build-up of pressure in the piston chamber 38 of prior switch devices to effect an undesired partial opening of the main contacts 11 and 14. The partial opening of the main contacts results in arcing therebetween with consequent burning and pitting thereof to eventually render the main contacts ineffective to properly engage to complete the motor armature circuit. In the apparatus shown herein, fluid leakage past the high pressure valve of the governor 2 ows via a pipe 59, passage 60, passage 61, volume 62 and port i63 to the piston chamber 38 where the slow build-up of Ipressure therein causes the piston 20 to move slowly to the right to compress the spring 40 and the trigger spring 47, but does not open the main contacts 11 and 14 due to the piston latch 22 being latched over the washer 37 on the circular lip 42, thereby preventing burning of the main contacts 11 and 14 with premature slight openings thereof. If the leakage is suicient to build up the pressure in the piston chamber 38 to a predetermined pressure, the main contacts will be opened as hereinafter described.

When the tluid pressure in the reservoir 5 and connected governor 2 builds up to a predetermined pressure (regulated as desired by the usual appropriate adjustment of governor settings), the governor high pressure valve snaps open in a -well-known manner to permit a sudden surge of high pressure to the pipe 59 and thence to the piston chamber 38. The sudden surge of uid pressure rapidly builds up to a predetermined pressure necessary to overcome the biasing forces of spring 40, causing the piston 29 to move to the right in the bore Z1 to engage the piston latch 22 which is held stationary by the lip 52 on washer 41, thereby resulting in compressing the spring 40 and at the same time compressing the trigger spring 47. Simultaneously with the compression of the trigger spring 47, the beveled surface 54 on the outer end of piston stem 36 engages and moves along the angular surface 55 on the piston latch 22 thereby moving the-lip 52 inwardly on the washer 41. When the fluid pressure in the piston chamber 38 attains a predetermined degree (determined by the biasing force of spring 40), the piston 2li and the piston stem 36 move sufficiently to the right to cause the beveled surface 54 thereof to move the piston latch 22 completely off the Washer 41 into engagement with tapered surface of the `Contact operating rod 45, thereby uncocking the piston latch and permitting the compressed trigger spring 47 to sharply snap the contact operating rod `45 and the piston latch 22 to the right, moving the contact arm 17 rapidly in a clockwise movement about pin 18 to open the main contacts 11 and 14 in a very rapid motion to limit the arcing therebetween. The clockwise movement of contact arm 17 is limited to a sutiicient degree by the movement of the pin 49 into engagement with the right side of the groove 50 in the piston stem 36.

From the above description it can be seen that there can be no partial slow opening of the main contacts 11 and 14 due to leakage of iluid in the piston chamber as has been the case in previous switch devices, the only type of opening being a fast complete snap opening when the fluid pressure in the piston chamber 3S is sufiicient to move the piston 2t) and piston stem 36 to the right far enough to unlatch or uncock the piston latch 22 to respond to the trigger spring 4'7.

With the main contacts 11 and 14 open, the circuit energizing the compressor motor 3 is interrupted, thereby stopping the compressor 4 until the pressure of fluid in the reservoir 5 is normally depleted through usage to a predetermined low pressure at which time the governor 2 operates in its usual manner to position the governor high pressure valve to vent the piston chamber 38 to atmosphere lto permit the spring 40 to return the piston 20 to the left-hand position with the stop 56 engaging the stop 57. As the piston is returned to the left-hand position as shown, the right-hand end of groove 50 shown in FIG. 2 in the piston stem 36 which is now in engagement with the pin 49, causes the contact operating rod 45 to move to the left, and thereby simultaneously moves the piston latch 22 to the left where the spring 53 latches lip 52 on the washer 41. The contact arm 17 is thus also returned in a counterclockwise direction to a position in which the main contacts 11 Iand 14 are reclosed. When the main contacts 11 and 14 are reclosed, the circuit for starting the motor 3 is again complete to start the compressor and thereby cause the reseating of the governor high pressure valve to permit normal operation of the compressor.

Having now described the invention, what I claim as new and desire to secure by Letters Patent, is:

1. An electric circuit controlling switch device comprising a stationary switch contact member, a movable switch contact member operable from a circuit-opening position out of engagement with said stationary switch contact member into a circuit-closing position engaging said stationary switch contact member and reversely, casing means having a chamber therein to which fluid under pressure may be supplied, a piston subjectable to the iluid pressure in said chamber and movable responsively to supply of fluid under pressure thereto and release of Huid under pressure therefrom to eiect operation of said movable cont-act member from its circuit-closing position to its circuit-opening position and vice versa respectively, and means operatively connecting said piston to said movable switch contact member to prevent movement of said movable switch contact member vfrom its circuit-closing position to its circuit-opening position until after said piston has moved a predetermined amount responsively to a build-up of uid pressure in said chamber.

2. An electric circuit controlling switch device comprising a stationary switch contact member, a movable switch contact member operable from a circuit-opening position out of engagement with said stationary switch contact member into a circuit-closing position engaging said stationary switch contact member and reversely, casing means having a chamber therein to which uid under pressure may be supplied, a piston subjectable to the fluid pressure in said chamber and movable responsively to supply of fluid under pressure thereto and release of uid under pressure therefrom to eiect operation of said movable contact member from its circuit-closing position to its circuit-opening position and vice versa respectively, latch means for locking said movable switch contact member in its circuit closing position, and cooperative cam means on said piston and said latch means whereby said b piston operates the latch means to unlock the movable switch contact member for operative movement out of its contact-closing position only after movement of said piston a predetermined amount responsively to fluid pressure build-up in said chamber.

3. An electric circuit controlling switch device comprising a stationary switch contact member, a movable switch contact member operable from a circuit-opening position out of engagement with said stationary switch contact member into a circuit-closing position engaging said stationary switch contact member and reversely, casing means having a chamber therein to which uid under pressure may be supplied, a piston subjectable to the fluid pressure in said chamber and movable responsively to supply of uid under pressure thereto and release of Huid under pressure therefrom to effect operation of said movable contact member from its circuit-closing position to its circuit-opening position and vice versa respectively, latch means for locking said movable switch Contact member in its circuit closing position, lost motion means connecting said piston and said movable switch contact member, and cooperative cam means on said piston and said latch means whereby said piston operates the latch means to unlock the movable switch contact member for operative movement out of its contact-closing position only after the movement of said piston a predetermined amount to an unlocking position responsively to fluid pressure build-up in Said chamber.

4. An electric circuit controlling switch device as claimed in claim 3, further characterized by spring means that is compressed by movement of said piston to a position for causing said cam means to unlock said latch means and eiective while so compressed upon such unlocking of said latch means for operating the movable switch contact member to its circuit-opening position with a rapid movement.

5. An electric circuit controlling switch device as claimed in claim 3, further characterized by spring means interposed between said casing means and said piston to yieldingly resist movement of said piston to said unlocking position and effective to restore said piston and said movable switch contact member to said circuit-closing position responsively to venting of iluid under pressure from said chamber.

6. An electric circuit controlling switch device as claimed in claim 3 further characterized by trigger spring means that is compressed by movement of said piston to a position for causing said cam means to unlock said latch means and eiective while so compresesd upon such unlocking of said latch means for operating the movable switch contact member to its circuit-opening position with a rapid movement, and other spring means interposed between said casing means and said piston to yieldingly resist movement of said piston to said unlocking position and effective to restore said piston and said movable switch contact member to said circuit-closing position responsively to venting of iluid under pressure from said chamber.

References Cited in the le of this patent UNITED STATES PATENTS 2,238,567 Prince Apr. 15, 1941 2,730,588 Kelle Jan. 10, 1956 2,730,589 Perry et al. Jan. 10, 1956 2,775,711 Kommer Dec. 25, 1956 

1. AN ELECTRIC CIRCUIT CONTROLLING SWITCH DEVICE COMPRISING A STATIONARY SWITCH CONTACT MEMBER, A MOVABLE SWITCH CONTACT MEMBER OPERABLE FROM A CIRCUIT-OPENING POSITION OUT OF ENGAGEMENT WITH SAID STATIONARY SWITCH CONTACT MEMBER INTO A CIRCUIT-CLOSING POSITION ENGAGING SAID STATIONARY SWITCH CONTACT MEMBER AND REVERSELY, CASING MEANS HAVING A CHAMBER THEREIN TO WHICH FLUID UNDER PRESSURE MAY BE SUPPLIED, A PISTON SUBJECTABLE TO THE FLUID PRESSURE IN SAID CHAMBER AND MOVABLE RESPONSIVELY TO SUPPLY OF FLUID UNDER PRESSURE THERETO AND RELEASE OF FLUID UNDER PRESSURE THEREFROM TO EFFECT OPERATION OF SAID MOVABLE CONTACT MEMBER FROM ITS CIRCIUT-CLOSING POSITION, TO ITS CIRCUIT-OPENING POSITION AND VICE VERSA RESPECTIVELY, AND MEANS OPERATIVELY CONNECTING SAID PISTON TO SAID MOVABLE SWITCH CONTACT MEMBER TO PREVENT MOVEMENT OF SAID MOVABLE SWITCH CONTACT MEMBER FROM ITS CIRCUIT-CLOSING POSITION TO ITS CIRCUIT-OPENING POSITION UNTIL AFTER SAID PISTON HAS MOVED A PREDETERMINED AMOUNT RESPONSIVELY TO A BUILD-UP OF FLUID PRESSURE IN SAID CHAMBER. 